What is the ruling on what resulted from Mustafa, who went out to help his friend Salim, and killed a person, while he did not know that Salim was a thief and that the reason for him being beaten was theft; is his action considered accidental killing or intentional killing?

Whoever kills a soul unjustly must offer sincere repentance. The blood money (diyah) is a compounded one, to be paid by his 'aqilah (male relatives on the father's side), because his act is considered akin to intentional killing (shibh 'amd) since he intentionally struck the deceased with an iron rod. He also owes expiation (kaffarah), which is freeing a believing slave; if he cannot find one, he must fast for two consecutive months. Some scholars are of the opinion that if he is unable to fast, he must feed sixty poor people.